Producing lead shapes



Patented Sept. 11 1962 3,053,654 PRODUCING LEAD SHAPES Paul A. McKim,Baton Rouge, La., assignor to Ethyl Corporation, New York, N.Y., acorporation of Delaware No Drawing. Filed Mar. 28, 1960, Ser. No. 17,8025 Claims. (Cl. 75-211) This invention relates to the manufacture of leadshapes. More particularly, the invention relates to the preparation ofsolid lead shapes or articles from finely divided lead, or essentiallylead systems, and especially lead systems derived from the preparationof organometallic compounds.

Although the general technique of forming solid shapes of metals fromfinely divided metals has been known for quite some time, it has been,for all practical purposes, not utilized for lead metal, probablybecause of the relatively low physical strength of the resultantproduct. It has recently been discovered that certain finely subdivided,essentially lead powders are highly suitable for making solid articles.These lead powders are derived from a reaction of an alkylating agentand an alloy of an alkali metal with lead, resulting in formation of alead tetraalkyl compound plus unreacted subdivided lead powder. Suchpowders are highly effective sources of subdivided lead metal forforming purposes. It has been found that by mechanically forming suchsubdivided lead, that solid shapes having surprising rigidity, tensilestrength, and other properties, can be readily made. Such formingoperations necessarily must be preceded or followed by treatment toeliminate minor quantities of the lead tetraalkyl component present,such component being a residual quantity which is not normally removedfrom the reaction product mixture. The removal of such minor impurities,prior to a mechanical forming operation, is an inconvenient andrelatively expensive operation. By this is meant that, although thetetraalkyl lead compound can be readily removed to a concentration lowenough to satisfy the economics of production of the tetraal'kyllead asa single product, considerable further treatment or effort is necessaryto remove and recover the tetraalkyllead to the point that the ultimatelead shape is perfectly innocuous. Further, it has been discovered thatthe presence, of even minor quantities of liquid tetraalkyl compoundsduring a forming operation provides a beneficial effect in that suchcomponents appear to assist and facilitate the actual forming operationas such. The reasons for this are not fully understood, but thetetraalkyllead liquid components appear to have an oiliness and alubricating eifect which apparently minimizes the mechanical effortrequired to form solid shapes from such subdivided systems. Hence, thetotal elimination of tetraalkyllead compounds, before forming, is not aparticularly satisfactory type of operation.

A general object of the present invention is to provide a new andimproved process for the formation of solid lead shapes. Moreparticularly, an object is to provide an improved process for forminglead shapes from finely divided lead residues from a process for makinga tetraalkyllead compound, said process being characterized by thereaction of an alkylating agent with a lead alloy and an alkali metal. Amore specific object is to provide a process producing lead solidshapes, employing the above mentioned feed solids wherein the benefitsof minor quantities of copresent tetraalkyllead components, upon theforming operation, are fully preserved, yet the ultimate solid leadshape is entirely freed of such materials. An additional object, ofcertain embodiments, is to provide a process wherein a portion only of atetraalkyl component is removed and recovered and the solids, uponfurther processing are formed into desired solid shapes, and theremainder of the tetraalkyl is entirely eliminated. A more particularobject is to provide in combination the synthesis of a finely dividedlead solids system or mixture, and a forming operation for producingsolid shapes therefrom. Other objects will appear hereinafter.

The process of the present invention comprises subjecting a finelydivided lead powder, consisting essentially of finely divided lead metaland accompanying minor quantities of tetraalkyllead compounds, toforming pressure operations at sufiiciently elevated pressures to formthe lead particles into an essentially homogeneous solid shape, andconcurrently with said operation heating the lead particles andaccompanying components to a temperature of from about C. to about 300C., for a time sufficient to essentially entirely thermally decomposethe tetraalkyllead components. When moving pressures are utilized, thedegree of movement can be varied and minimized by an appropriateincrease in the forming pressure. In certain instances, entirely staticpressures, i.e., with no movement of the lead powders other than thataccompanying bulk volume reduction are employed. In virtually all cases,pressures of about 5000 pounds per square inch and above are employed.The duration of the temperature application will vary with theparticular identity of the tetraalkyllead impurity or component, theconcentration, and the intensity of temperature applied to the systemduring the processing. When lower temperatures, in the neigh' borhood ofl00 or are applied, and in the case of, for example, tetraethyllead,temperature applications of as high as an hour may sometimes berequired, although usually 30 minutes is quite ample for mostconcentrations. On the other hand, when temperature levels of 200 to 300C. are applied, the duration of such application can be as low asseveral seconds to about 10 minutes.

The general mode of operation, and the best manner of carrying out theinvention, will be fully understood from the working examples anddetailed description hereinafter.

Example I This example illustrates preparation of the charge stock forthe present process by chemical means. 100 parts of monosodium leadalloy, NaPb, were charged to an autoclave along with about 50 parts ofethyl chloride, this amounting to approximately 75 percent excess ethylchloride. The mixture was reacted at an autogeneous pressure at elevatedtemperature until the action was terminated, as shown by a decrease intemperature and pressure. The product of this reaction was an apparentlydry reaction mixture containing about 55 weight percent lead, 24 percenttetraethyllead, and 20 percent sodium chloride. Excess ethyl chloridewas vented during the reaction and upon completion of the reaction. Theresultant dry granular material was then discharged from to steamdistillation for a suificient period of time to re- 'move a largeproportion of the tetraethyllead component. The resultant material is amultiphase mixture of the subdivided lead particles, sodium chloride(largely dissolved in the aqueous phase) and minor quantities oftetraethyllead, in a concentration usually, of the order of severalpercent, based upon the lead.

Screening a portion of this material, in US. standard screens, gives thefollowing size distribution:

about 5 minutes. A finely grained lead solid, virtually free oftetraethyllead, is produced. In preferred embodiments of this example,the temperature gradient is applied so that a higher temperature isprovided at the exggg gg Screen N trusion end of the chamber and lowertemperatures are Retained of Screen applied in the chamber proper. Thistechnique provides Openings the benefit of retaining the alkyl lead ortetraethyllead component unchanged during a large portion of the procg52 8-8233 essing, and thus assures a lubricating effect derived from 2535 010197 10 the tetraethyllead component. The accompanying Water 2; 38- with the change stock is concurrently vaporized from the 73 120010049 system and is removed by blowby past the ram, and to a 3% 332888%? certain extent by vaporizing through the die apertures. Inaddition to rolling and extrusion as exhibited in the above examples,the forming operations employed in- The lead powder, prepared as abovedescribed, is then elude dlTeCt pr ssing of the lead powder charged rn afed to a rolling mill operation, being fed on a steel con- Press 1119Mor (he havmg desn'ed final part configura' veyor belt threaded through apair of pressing Tons tron, wh1ch can be, for example, forms for radator orna- Heating means, which are typically gas burners positionedments, name Parts for Tallroad and ,Shlp models below the steel belt,are provided slightly before the en- 0 and Q artlcles- T e followrngexample illustrates the trance to the rolling operation and providesufiicient heat techmque employed m such mstancesto raise thetemperature of the subdivided solids to about Example Ill 250 C. Inassing through the rolls, a ressure a roximating 5000 gounds per squareinch is agplied, the ctual g Powder employed. Is as i Exanjlp 16 I atime of contact between the rolls being about minute. Specimens of iPowder mserted m a dle or.mol The duration of the temperature indicated,of the order prfmdmg cyhndncal .bushmg pattern Pressure 15 apof about Cis about 3 minutes. A Subsequent plied thereto by a matrngram, at apressure of about longer period is provided as the charge material islowpounds per Square Inch E the mold ered in temperature to about 100,this period requiring 1s heated to a tempefratire of 115 i i g usuallyabout 7 to 10 minutes. The indicated processing temperature aremall/tamed i P g y g results in the formation of a thin lead strip,essentially i i t the termmatw? of i t e angled free of tetraalkyl lead,and having very good surface gloss mg 15 discharged fr he 2 E asfsmoot1: or finish, as well as being a stiff, sturdy material, having andsharp configuratlons. na ysls of ragment to en tensile strength of theorder of 4000 to 6000 pounds per from the shape shows virtually nodetectable onganolead square inch. The degree of reduction of crosssectional component E I IV thickness accomplished during the actualrolling is subxamp e ject to easy adjustment. In typical operations, theaver- In this operation, the lead powder was derived genage thickness ofthe lead powder feed stream is from erally as obtained in the precedingexamples, but the about /a to about A inch, and the pressing operationrecomposition thereof differed in that it contained approxisults in athickness reduction of from 50 to 90 percent, a 40 mately 6 weightpercent tetraethyllead and about 11 typical sheet having a thickness ofabout 0.04 inch. percent water. The material was charged to an extrusionExample H chamber, and a pressure of about 15,000 pounds per square inchis applied, employing an extrusion ratio of In this example, the samefeed supply is used, as in about 35. The extrusion chamber and contentsare Example I, but instead of rolling the lead powder, it is heated to atemperature of about 190 C., resulting in charged to an elongatedcylindrical extrusion chamber, rapid decomposition of the tetraethylleadcomponent and having a die at one boundary thereof, the chamber andvaporizing of the water phase, which was discharged in die providing anextrusion ratio of the order of 42. The part as a vapor dischargedbackwards past the extrusion die is in the shape of a cylindrical orcircular aperture of ram and to a minor extent, by concurrent dischargeabout 0.4 inch in diameter. Pressure of about 25,000 through the dieorifice. The residence time of the mapounds per square inch is applied.Concurrently with apterial in process, in the extrusion chamber, isabout 3 plying the pressure, the extrusion chamber is heated by minutes,and approximately 5 to 10 minutes additional external means, typically aresistance wire winding, or in time is required for the solid leadproduct to cool to a some cases, an induction heating coil, to heat thechamber temperature of below 100 C. The product is a dry, and thecontents to. about 175 C. Upon application of substantially homogeneousbar, having virtually no tetrapressure to the charge, by a ram in theextrusion cham ethyllead as such therein. her, a substantiallyhomogeneous, cylindrical shape is In addition to the foregoingoperations, additional forced through the die, at a temperatureapproximating working examples are summarized in the following table:

Composition of Feed Forming and Treating Example Alkyllead Wt. Size ofSolids Technique Pressure Temper- Dura- Percent (p.s.i.) ature, O. tionMin.

Tetra-n-butyl lead.... 5 Through on 200. Rolling... 4, 000 140 2 Tetra-1Propyl lead. 5 Through 100- on 325. Extrusion- 10,000 130 4Tetra-isoamyllead..-. 7 Through 35, on 100-. Pressing... 28,000 7 Methyltriethylleadn 2 Through 18.. .do..... 17,000 8 D1rnethyl-diethyl.--- 1.5Through 18.- Rolling... 15,000 130 3 Methyl-triethyl lead-- 0.5 Through18.. Extrusion- 20,000 5 1 Screen numbers refer to U.S. Sieve Series. 2Refers to time under pressure or in processing; additional time alsorequired in cooling to below 100 0.

As heretofore mentioned, the present forming operations can be carriedout in conjunction with preceding C. The duration of residence time inthe extrusion chamber and the die is up to about several minutes, andthe formed lead shape retains the temperature, or a temperature of about100 C. for an additional period of recovery operations of similarcharacter.

In other Words,

an intermediate forming operation is directed to a partial removal of aco-present tetraethyllead, providing an intermediate solid shape havingappreciable quantities of alkyl lead therein, and such shape is thenfurther mechanically shaped by pressure application concurrently withthermal decomposition as in the preceding examples. An illustration ofsuch embodiment follows.

Example XII A reaction mixture is prepared by reacting sodium lead alloyand ethyl chloride, as in Example I. Only a portion of thetetraethyllead is removed by steam distillation, however, reducing theconcentration thereof to about 15 percent of the lead.

The solids containing residue is (free drained leaving a wet powdercontaining mixture with the indicated proportions of tetraethyllead andcomparable amounts of aqueous phase. Portions of the mixture are pressedat ambient temperature. This initial pressing is in a cylindricalchamber, by application of pressure by a ram. Suflicient clearances areprovided to allow discharge of liquid phases past the ram or plunger.Upon application of pressure of about 5000 pounds per square inch, asolid appearing shape is formed, having roughly about 3 weight percenttetraethyllead and comparable proportions of water or aqueous phase.

The solid shapes, as above formed, are then charged to an extrusionchamber and processed as in Exhibit II, except that the extrusionorifice in this instance is in the form of a thin strip shape. As inpreceding exmaples, this operation is accompanied by heating to atemperature of, typically 150 C., to provide complete decomposition ofthe tetraethyllead content.

It will be apparent from the foregoing examples that the principles ofthe present invention are applicable to a substantial number ofparticular systems, and that a variety of forming techniques can beemployed.

As evident from the examples, in all instances a substantial temperatureof above 100 C. and below about 300 C., is employed for the process. Thedecomposition of the alkyl lead compounds varies in rapidity accordingto the particular identity of the particular alkyl lead and according tocertain other factors, e.g., concentration. In the case oftetraethyllead, measurable decomposition occurs in the neighborhood of100 C., but the rate is quite low, particularly when minor quantities ofthermal decomposition inhibitors are present in solution in a solutionin a tetraethyllead. Ordinarily then, and particularly because of asupplemental stabilizing eifect of solids present, a temperature ofabove about 130 C. is preferred for this particular material. However,temperatures, as indicated, of the order of above 110 or 115 C. arequite suitable and if the temperature level is maintained for asufficient period of time, full decomposition of the organolead materialis accomplished. The tetraalkyllead compounds having alkyl groups ofmore than two carbon atoms are more easily decomposed than thetetraethyllead. Tetramethyllead, on the other hand, is quite refractoryin its resistance to thermal decomposition, and when this is thecomponent present, temperatures approaching the range of about 290 to300 C. are ordinarily preferred to accomplish this result.

The alkyl lead compounds, under the conditions of the present process,do not decompose violently. It appears that the relatively largeproportions of lead solids, plus the co-presence, usually, of an aqueousphase, results in a distinct moderation of the potential severity ofdecomposition. Although alkyl lead compounds with higher alkylsubstituents are more readily decomposed, the compounds with lower alkylsubstituents are more apt to exhibit violent decomposition. Hence, inthe case of the latter, it is highly preferred that the alkyl leadconcentration should not exceed about 5 percent.

The time necessary to process and maintain temperature during theprocessing at the desired level necessary for decomposition, will dependto some extent upon the proportions of the alkyl lead compound, upon itsidentity, and by the temperature level applied. Heating and coolingperiods, to and from the highest temperature of a process, alsocontribute to the decomposition. The overall processing times, in whichtemperatures of over 100 C. prevail, are usually from 1 to 15 minutes.However, by increasing the temperatures during actual pressure formingoperations, the necessary pressure period can be drastically reduced.Thus, by increasing the maximum temperature, during Example III, toabout 200 C., the pressure application period can be reduced to severalseconds. Similar reductions in time are attainable in the otherexamples.

The actual pressures employed in forming the lead shapes will dependupon the degree of compacting actually desired and the mode or techniqueemployed in the forming. As clear from the above examples, suitablepressure ranges are from the range of several thousand to about 30,000pounds per square inch, although these are not explicitly limiting. Apreferred range is from about 10,000 to about 20,000 pounds pressure.

The particular weight concentration of the lead alkyls is not highlycritical. It is preferred that the lead powder feed contain not overabout 5 weight percent of the alkyl lead component, but the process isequally operable with higher concentrations of the order of 7 or even upto about 10 weight percent. In these instances, a portion of the alkyllead component is actually dislodged from the feed material under theinfluence of the pressure alone, and may be recovered as such. When theconcentration is of the order of about 1.5 or 1 percent or lower,virtually all the removal of the alkyl lead is by the mechanism ofthermal decomposition as above described.

Having fully described the invention in the several modes of operation,what is claimed is:

1. The process for forming solid lead shapes comprising forming, byapplication of pressure of at least about 5,000 pounds to about 30,000pounds per square inch, a solid shape from a finely dividedpredominantly lead powder, said powder consisting essentially of finelysubdivided lead and from about 0.5 to 10 weight percent of atertaalkyllead compound, and concurrently with said pressure formingoperation, heating to a temperature of above about 100 to about 300 C.for a time sufiicient to thermally decompose the tetraalkylleadcompound.

2. The process of claim 1 further defined in that the pressure is staticpressure applied to the lead powder in a forming die.

3. The process of claim 1 further defined in that the pressure isapplied to the lead powder by forming rolls.

4. The process of claim 1 further defined in that the lead powder ischarged to an extrusion chamber and pressure is applied to force a solidshape through a forming die in the boundary of said chamber.

5 The process comprising, in combination, reacting an alkali metal leadalloy with ethyl chloride, forming thereby a reaction product includingtetraethyllead, excess lead in finely divided form, and alkali metalchloride, separating substantially all the alkali metal chloride and thepreponderance of the tetraethyllead therefrom, thereby forming finelysubdivided lead powder accompanied by minor quantities of from about 0.5to 5 percent of tetraethyllead, then subjecting said powder to a formingoperation including application of pressure of at least 5,000 pounds persquare inch and concurrently heating to a temperature of above about 100to about 300 C. for a time suflicient to thermally decompose the,tetraethyllead, whereby a solid shape substantially free oftetraethyllead is produced.

1. THE PROCESS FOR FORMING SOLID LEAD SHAPES COMPRISING FORMING, BYAPPLICATION OF PRESSURE OF AT LEAST ABOUT 5,000 POUNDS TO ABOUT 30,000POUNDS PER SQUARE INCH, A SOLID SHAPE FROM A FINELY DIVIDEDPREDOMINANTLY LEAD POWDER, SAID POWDER CONSISTING ESSENTIALLY OF FINELYSUBDIVIDED LEAD AND FROM ABOUT 0.5 TO 10 WEIGHT PERCENT OF ATERTAALKYLLEAD COMPOUND, AND CONCURRENTLY WITH SAID PRESSURE FORMINGOPERATION, HEATING TO A TEMPERATURE OF ABOVE ABOUT 100 TO ABOUT 300* C.FOR A TIME SUFFICIENT TO THERMALLY DECOMPSOE THE TETRAALKYLLEADCOMPOUND.